The Human Genome Project is a concerted effort of the scientific community. In order for this project to be completed, it will require the development of new technologies and the optimization of old technology. Interspecific hybrids have been utilized for a number of years for gathering physical localization data. With the development of recent technology, it is apparent that interspecific hybrids are not only useful for mapping genes but for constructing physical maps of human chromosomes. We propose to utilize three types of interspecific hybrids to construct a physical map of human chromosome 2. The first type will be prepared from patients with known translocation breakpoints on human chromosome 2. These hybrids will be used to establish the framework for the map. The second class of hybrids will be constructed using microcell-mediated chromosome transfer. Microcell hybrids containing fragments of human chromosomes will be utilized to gather regional localization data. The third class of hybrids will be radiation-reduced hybrids. To construct these hybrids, microcell hybrids containing an intact human chromosome 2 will be irradiated and fused to rodent cells. All three classes of hybrids will be utilized to produce a physical map of human chromosome 2. In addition, the microcell hybrids and the radiation-reduced hybrids will serve as a useful source of DNA for constructing recombinant DNA libraries specific for any region of the chromosome.